The pyrazolone couplers often used in silver halide photographic elements such as color reversal films exhibit rather broad dye hue, unwanted blue absorption and are reliant upon formaldehyde stabilization for image permanence. Bicyclic azole couplers including pyrazolotriazole couplers such as 1H-pyrazolo-[5,1-c]-1,2,4-triazoles and 1H-pyrazolo-[1,5-b]-1,2,4-triazoles are attractive couplers to replace these pyrazolone couplers because they yield narrower dye hue, better thermal stability without reliance upon formaldehyde and less unwanted absorption.
Because image dyes with narrow-bandwidth spectral absorption afford less unwanted absorption (i.e. absorption of light in the "wrong" regions of the visible portion of the electromagnetic radiation") than broader band pyrazolone couplers, improved color rendition is more readily achieved. Excessive image-dye unwanted spectral absorptions can cause colors to be reproduced darker and to exhibit lower colorfulness than in the original scene unless compensations are made in other aspects of the film affecting color reproduction. Various means have been used typically in photographic color reversal films to overcome the color reproduction effects of unwanted spectral absorptions of image dyes. Such means can include increases in the contrast of reproduced images relative to the original scene, which generally improves the colorfulness of reproduced colors, but can be at the expense of tone reproduction. That is, the dark parts of the reproduced image can appear too dark and the light parts of the reproduced image can appear too light. Further means for overcoming the color reproduction effects of image-dye unwanted absorptions can include widely separating the film's red-light, green-light, and blue-light spectral sensitivity characteristics along the visible wavelength axis, which again generally improves the colorfulness of reproduced colors, but this can be at the expense of inducing errors in reproduced hue and lightness. For example, one trade-off of widely separated film spectral sensitivities is that metameric colors in an original scene (i.e. visually-matched color stimuli having different spectral compositions) may no longer look alike in the reproduction. Still further means for overcoming the color reproduction deficiencies of image-dye unwanted absorptions can include incorporation of high levels of inter-image effects in order to obtain satisfactory color reproduction, but these high levels may well be difficult or impossible to achieve. Typically a combination of means for overcoming the color reproduction deficiencies of image-dye unwanted spectral absorptions is incorporated in photographic color films and is adjusted so that color-reproduction trade-offs are minimized, insofar as possible, for colors regarded as those most often encountered in practice and weighted according to their relative importance and to the tolerance of different types of trade-offs for those colors.
A photographic color film having an image dye with narrow spectral absorption bandwidth would have the advantage of exhibiting to a lesser degree the aforementioned color reproduction deficiencies associated with excessive unwanted spectral absorptions, and thus require less of the aforementioned color-reproduction compensations. A further advantage of such a film then is that, by requiring a lesser degree of color-reproduction compensations, the aforementioned color-compensation tradeoffs are induced to a lesser extent, resulting in reproduced images regarded generally as having improved color reproduction compared to films known in the art having image dyes of broad spectral bandwidth.
It is not uncommon for the images reproduced on photographic color films to in turn serve as original images in subsequent imaging operations such as in the production of duplicate photographic transparency images, the production of photographic color reversal reflection prints, the production of photographic color inter-negatives, and in the scanning of said photographic color film images for digital imaging operations carried out on computers.
U.S. Pat. Nos. 5,609,996 and 5,985,533 suggest employing certain pyrazolo azole couplers that are useful for producing magenta dyes having improved dye light stability.
Commercially available photographic color reversal film duplicating media and scanning devices have spectral sensitivity or spectral response characteristics and associated chemical or digital color-signal processing optimized for use with commercially available input photographic color reversal film originals having pyrazolone couplers. Thus an improved photographic color reversal film with narrower bandwidth magenta dye and reduced color-compensation trade-offs may not function compatibly with said photographic color reversal film duplicating media and scanning devices. For example, a grayscale produced on a color reversal film with narrower bandwidth magenta dye may produce different color-balance or color-contrast results when duplicated or scanned using the aforementioned existing photographic duplicating media or scanning devices than would a visually matched grayscale produced on a commercially available input photographic color reversal film having pyrazolone couplers would using said photographic duplicating media or scanning devices. Therefore compatibility of the narrow bandwidth magenta dye with a given pair of cyan and yellow dyes requires more attention to the choice of magenta absorption maximum wavelength, .lambda.max, than with a broad magenta dye. That is, to be compatible with a broad range of color scanners and commercially available color reversal film duplicating media, the narrow bandwidth magenta dye .lambda.max must be carefully chosen. Due to the combined requirements of color reproduction in the original film, color reproduction of subsequent duplication processes of the original film, and color-film scanner compatibility, a magenta dye with the following spectral features would be useful for many applications such as color reversal applications:
spectral half-bandwidths in the range 72-84 nm and more preferably 76-82 nm, and PA1 a .lambda.max value in the range of 553-560 nm and more preferably 554-558 nm. PA1 BA represents a bicyclic azole coupler nucleus with --(C(R.sup.1)(R.sup.2)).sub.P -- bonded to a ring carbon in a non-coupling position of the coupler nucleus; PA1 p is 1 or 2, and each R.sup.1 and R.sup.2 is independently selected from H and a substituent group, provided that any two of R.sup.1 and R.sup.2 may join to form a ring; PA1 R.sup.a and R.sup.b are each independently selected from H and a substituent group, provided that substituent groups may join to form a ring; PA1 each Y is an independently selected substituent and m is 0-4; PA1 X is selected from the group consisting of --C(O)--, --S(O).sub.2 --, --S(O)--, and --P(O)(OH)--; PA1 W is a connecting group having a chain of up to four atoms between X and Z, and n=0 or 1; and PA1 R.sup.5 is H or a substituent group and R.sup.6 is a substituent bonded to --NH-- by an electron withdrawing group in R.sup.6 ;
Color reversal films commonly contain relatively high silver halide levels and are processed in such a way that the dye yield (moles of dye formed per mole of reduced silver) is significantly less than 100%. The low dye yield affords images with low graininess, and is caused by components present in the color developer that compete with the image coupler for oxidized developer. The competing components include hydroxide ion, present in relatively high concentration due to the higher pH of the color developer employed in reversal processing.
As a consequence of the relatively high color developer pH, color reversal films, typically exhibit a negative dependence of dye density on developer pH. That is, negative slopes of D.sub.max vs. color developer pH are common in color reversal systems. This negative slope is caused by the reaction of oxidized developer with hydroxide ion which competes with the dye-forming reaction of oxidized developer with image couplers possessing low pK.sub.a. In a color reversal film, a magenta coupler that exhibits a positive pH dependence is likely to cause color balance shifts under conditions of variable developer pH if the cyan and yellow couplers have the typically negative pH dependencies. If the cyan and yellow couplers employed exhibit negative pH sensitivities, as they commonly do, a bicyclic azole coupler which also exhibits a negative slope would be desirable. Unfortunately, it is common for couplers of this class to exhibit a positive slope in plots of D.sub.max vs. color developer pH, presenting a disadvantage for use in color reversal films.
An optimal color reversal film would have couplers in all three color records that are pH insensitive. Therefore, magenta couplers with flat pH sensitivity are also desirable. The couplers of this invention possess color developer pH sensitivities that exhibit either a small negative slope or a very slight positive slope. Those with negative pH sensitivity can be combined with common color reversal cyan and yellow couplers that typically exhibit matching negative sensitivities. Those magenta couplers that have virtually flat pH sensitivity could be combined with matching pH-insensitive cyan and yellow couplers. The green D.sub.max obtained for a film processed in a pH 11.60 color developer is subtracted from the green D.sub.max for the same film processed in a pH 12.20 color developer to yield a .DELTA.D.sub.max metric. For the present invention, the coupler structures achieve pH sensitivities commonly in the range -0.30 to +0.10. Useful magenta couplers with negative pH sensitivities possess .DELTA.D.sub.max nominally in the range of -0.30 to -0.10, while useful magenta couplers with "flat" pH sensitivities possess .DELTA.D.sub.max in the range of -0.10 to +0.10.
A problem to be solved is to provide a silver halide photographic element that produces images having improved color rendition.